The objective of this project is to examine the hypothesis that specific factors in the cellular environment surrounding neurons and their processes are major determinants of the success or failure of axonal regeneration in the vertebrate central nervous system. Experiments will be performed to determine the ability of grafted neurons and non-neuronal cells to provide trophic influences and appropriate cellular substrates which may stimulate and sustain axonal regeneration in the CNS of mammals and amphibians. By means of freeze-fracture and thin section electron microscopy, the membranous features of reactive astrocytes and the interaction between growing neurites and non-neuronal cellular elements will also be examined. Using a tissue culture model consisting of enriched populations of astrocytes and co-cultured neurons, studies will be undertaken: (1) to define the effect of astrocytes on axonal outgrowth; (2) to determine whether these glial cells produce a "neuronotrophic," NGF-like factor; and (3) to examine the mitogenic effect of axonal and myelinic constituents on astrocytes. By means of combined tissue culture, immunocytochemical, autoradiographic and tissue grafting approaches, attention will also be focused upon cellular mechanisms associated with the development of glial scars. In particular, the hypothesis that the mechanical impermeability of the astroglial scar is specifically related to the establishment of an astrocytic basal lamina will be further explored. Finally, cytochemical comparisons will be made to determine qualitatively whether variations in glycosaminoglycans composition of the extracellular matrix could account for differences in cellular mobility and axonal outgrowth observed in the amphibian and mammalian CNS after injury.